7.3. The Message Content-Type (original) (raw)

Connected: An Internet Encyclopedia
7.3. The Message Content-Type

Up: Connected: An Internet Encyclopedia
Up: Requests For Comments
Up: RFC 1521
Up: 7. The Predefined Content-Type Values

Prev: 7.2.6. Other Multipart subtypes
Next: 7.3.1. The Message/rfc822 (primary) subtype

7.3. The Message Content-Type

It is frequently desirable, in sending mail, to encapsulate another mail message. For this common operation, a special Content-Type, "message", is defined. The primary subtype, message/rfc822, has no required parameters in the Content-Type field. Additional subtypes, "partial" and "External-body", do have required parameters. These subtypes are explained below.

  NOTE: It has been suggested that subtypes of message might be
  defined for forwarded or rejected messages.  However, forwarded
  and rejected messages can be handled as multipart messages in
  which the first part contains any control or descriptive
  information, and a second part, of type message/rfc822, is the
  forwarded or rejected message.  Composing rejection and forwarding
  messages in this manner will preserve the type information on the
  original message and allow it to be correctly presented to the
  recipient, and hence is strongly encouraged.

As stated in the definition of the Content-Transfer-Encoding field, no encoding other than "7bit", "8bit", or "binary" is permitted for messages or parts of type "message". Even stronger restrictions apply to the subtypes "message/partial" and "message/external-body", as specified below. The message header fields are always US-ASCII in any case, and data within the body can still be encoded, in which case the Content-Transfer-Encoding header field in the encapsulated message will reflect this. Non-ASCII text in the headers of an encapsulated message can be specified using the mechanisms described in [RFC-1522].

Mail gateways, relays, and other mail handling agents are commonly known to alter the top-level header of an RFC 822 message. In particular, they frequently add, remove, or reorder header fields. Such alterations are explicitly forbidden for the encapsulated headers embedded in the bodies of messages of type "message."

Next: 7.3.1. The Message/rfc822 (primary) subtype

Connected: An Internet Encyclopedia
7.3. The Message Content-Type